1. Field of the Invention
This invention relates to hydrocarbon processing utilizing a solid phosphoric acid catalyst. More particularly, the invention relates to an improved process for removing spent solid phosphoric acid catalyst from a reactor without generation of toxic dust or highly acidic washings.
Solid phosphoric acid catalyst is comprised of phosphoric acid absorbed on a suitable solid carrier material. The catalyst is used in the petroleum refining and petrochemical industries to promote polymerization or combination of olefinic hydrocarbons, for example to polymerize normally gaseous olefins to produce gasoline boiling range liquid product. Petrochemical uses include production of cumene from propylene and benezene, and hexene, heptene, nonene and dodecene from propylene and/or butylene.
The activity of such solid phosphoric acid catalysts declines with use, and the catalyst must periodically be removed and disposed of.
2. The Prior Art
In the past, spent catalyst has often been dumped from a reactor and placed in a landfill, or in some cases slurried for disposal in wastewater. In some cases, spent catalyst has been neturalized with basic material after being dumped from the reactor but prior to disposal. These prior art disposal techniques are not entirely satisfactory from safety and environmental standpoints, as dumping of spent unneutralized catalyst from a reactor generates considerable toxic dust, and slurrying spent catalyst generates acidic washings which create safety and environmental problems.
U.S. Pat. No. 2,369,693 to Tollefson describes a method of regenerating spent phosphate catalyst by burning carbonaceous matter off the catalyst in the presence of amonia. The catalyst described in this reference is ammonium phosphate rather than phosphoric acid, and the regeneration by burning is not similar to the neutralization step of the present invention.
U.S. Pat. No. 4,436,900 to Matsuzaki et al describes deactivating a catalyst with ammonia to stop a reaction at a desired point. Again, this reference does not deal with neutralization of spent catalyst prior to disposal.